1. Field of the Invention
This invention relates to a novel recording liquid (hereinafter referred to as ink), particularly an ink suitable for a system in which recording is performed by ejecting the ink from fine ejection outlets (ejection orifices) provided at the recording head and permitting the ink to fly as liquid droplets.
2. Description of the Prior Art
For writing implements (fountain pens, felt pens, etc.) for performing recording on a recording medium such as paper, solutions of various dyes dissolved in water or other organic solvents have been used in the prior art.
Also in the so-called ink jet system in which the ink within the recording head is ejected from ejection orifices by action of a piezoelectric vibrator or by electrostatic attraction caused by application of high voltage, etc., inks comprising various dyes dissolved in water or organic solvents have been used. However, as compared with inks for use in stationary such as a fountain pen or a felt pen, the ink for ink jet is demanded to have characteristics to meet further strict conditions.
Such an ink jet system performs recording by permitting droplets of the so-called ink to fly and by attaching them onto a recording medium. Such an ink comprises a recording agent (a dye or a pigment) and a liquid medium for dissolving or dispersing the agent (water or an organic solvents, or their mixture) as the basic components, optionally containing an additive added therein.
In the prior art, as such a kind of ink, for example, there have been known solutions or dispersions of various dyes or pigments in aqueous or non-aqueous solvents as disclosed in Japanese Patent Publication Nos. 8361/1975, 40484/1976, 13126/1977 and 13127/1977 and Japanese Patent Laid-open Publication No.95008/1975. Preferable characteristics of this kind of ink may include the following:
(1) the ink should have the properties of liquid (viscosity, surface tension, electroconductivity, etc.) matching to the ejection conditions (driving voltage, driving frequency of piezoelectric element, shape and material of orifice, orifice diameter, etc.);
(2) the ink should be stable during storage for a long term so as not to cause clogging of fine ejection outlets or capillary pores;
(3) the ink should be fixed rapidly onto a recording medium (paper, film, etc.) with smooth circumference of ink dots and little feathering;
(4) the ink should give a printed image with sharp tone and high optical density;
(5) the ink should give a printed image excellent in fastness such as water resistance, light resistance, etc.;
(6) the ink should not corrode materials coming into contact with the ink (the vessel, the connecting tube, the sealing material, etc.);
(7) the ink should be excellent in safety such as from odor, toxicity, inflammability, etc.;
(8) the ink should be stable to heat for the use in the device as described above in which liquid droplets are generated by giving thermal energy to the recording liquid; etc.
It is considerably difficult to satisfy such various characteristics as mentioned above at the same time. The prior art as described above was unsatisfactory in this respect.
Since the ink to be applied to recording for such purpose is composed basically of a dye and its liquid medium, the above ink characteristics will be greatly governed by the inherent properties of the dye. Accordingly, the selection of a dye having the above characteristics is an extremely important technique in this field of art.
Particularly, it is extremely difficult to select a dye from among existing dyes which can satisfy all of the characteristics of water resistance, light resistance and tone. For example, a direct dye having good water resistance is not sharp in tone, while an acidic dye having sharp tone is inferior in light resistance, and a metal containing dye having good light resistance is not sharp in tone.
Thus, the present invention has been accomplished as the result of extensive investigation to find a dye suitable for the ink to be used for such purpose.